One of the major determinants of tropism of any virus is the interactions with cell surface molecules and the subsequent entry. The overall objective is to decipher the molecular events of HHV-8 target cell interactions vital for virus entry and infection, and to define the molecular basis for HHV-8's role in the pathogenesis of KS. HHV-8 enters the endothelial, B, and fibroblast cells via endocytosis. HHV-8 binds to the ubiquitous cell surface heparan sulfate (HS)-Iike molecules via its envelope glycoproteins gB and gpK8.1A, interacts with the cell surface alpha3beta1 integrins via its gB, utilizes it as one of the entry receptor, and induces the phosphorylation of integrin-dependent focal adhesion kinase (FAK). Since activation of FAK, Src-family kinases, and other kinases is central to many paradigms of outside-in signaling by integrins, actin assembly and endocytosis, we hypothesize that by its interaction with integrins, HHV-8 takes advantage of the pre-existing FAK and the associated signaling pathways to promote its entry, to deliver its genome into the nucleus and to modulate a cellular state facilitating the infection. Our studies show the activation of key mediators of integrin-induced signal pathways such as FAK, Src, Shc, PI-3K and RhoGTPases by the purified HHV-8. Purified soluble HHV-8 gB also inducted the FAK dependent target cell adhesion, and integrin-dependent FAK-Src-PI-3K-RhoGTPase signal pathways and cytoskeletal rearrangements. In an integrin-FAK-dependent manner, HHV-8 also activated the PI-3K-PKC-delta,-MEK-ERK signal pathway. To test our hypothesis further, the focus of this grant is to define the role of HHV-8-induced key signal mediators such as FAK, Src and PI-3K in HHV-8 entry into the target cells, subsequent movement in the cytoplasm and delivery of viral DNA into the nuclei of infected cells, and two specific aims were formulated: 1.To define the role of HHV-8 induced FAK, Src and PI-3K in the entry of virus into the target cells. 2. To define the role of HHV-8 induced FAK, Src, PI-3K and RhoGTPases in the migration of capsid/tegument in the cytoplasm of the infected cells and in the delivery of viral genome to the nucleus. These studies are significant since they will provide an insight in the biology of HHV-8 interactions with the host cells. Further understanding of HHV-8-cell signaling will broaden our knowledge of HHV-8 related diseases and eventually lead to new anti-HHV-8 agents, and therapeutic agents against KS.